1. Field of the Invention
The present invention relates to an induction motor, and particularly, to an induction motor controller.
2. Description of the Conventional Art
FIG. 1 is a view schematically showing a construction of an induction motor in accordance with the conventional art.
As shown in FIG. 1, the induction motor in accordance with the conventional art largely includes: a stator 100; an induction rotor 120; a permanent magnet rotor 150; and a rotating shaft 140.
The stator 100 is made up of four stator coils 160A, 160B, 160C and 160D respectively wound around an iron core 110 of the induction motor. Also, to generate an elliptical rotating magnetic field in the stator 100, four shading coils 170A, 170B, 170C and 170D are spatially disposed at regular angles on the iron core 110 at which the stator coils 160A, 160B, 160C and 160D are installed. Here, the four stator coils 160A, 160B, 160C and 160D are sequentially connected in series in order that the coils adjacent to each other have the same polarities.
The permanent magnet rotor 150 consists of a ring type permanent magnet (not shown) installed between the stator 100 and the induction rotor 120 at a predetermined gap and a permanent magnet supporting unit (not shown) for supporting the ring type permanent magnet. Also, to make the permanent magnet rotor 150 rotated centering around the rotating shaft 140, a bearing 130 is installed between the permanent magnet supporting unit and the rotating shaft 140.
Hereinafter, an equivalent circuit of the induction motor in accordance with the conventional art will be described with reference to FIG. 2.
FIG. 2 shows an equivalent circuit of an induction motor in accordance with the conventional art.
As shown in FIG. 2, the stator coils 160A, 160B, 160C and 160D of the induction motor in accordance with the conventional art are connected in series with each other, and the power (AC) is directly applied to the stator coils 160A, 160B, 160C and 160D. Here, to operate the induction motor with high efficiency, the winding number of the stator coils 160A, 160B, 160C and 160D of the induction motor is designed so as to be suitable for high efficiency features. Namely, in order to operate the induction motor with high efficiency, the winding number of the stator coils 160A, 160B, 160C and 160D is determined according to the power (AC).
Moreover, if the power (AC) is supplied to the stator coils 160A, 160B, 160C and 160D of the induction motor in accordance with the conventional art, the stator coils 160A, 160B, 160C and 160D generate magnetic fields. According to the magnetic fields generated by the stator coils 160A, 160B, 160C and 160D, the shading coils 170A, 170B, 170C and 170D generate magnetic fields. At this time, the stator 100 generates an elliptical rotating magnetic field obtained by composing the magnetic fields generated by the stator coils 160A, 160B, 160C and 160D and the magnetic fields generated by the shading coils 170A, 170B, 170C and 170.
The elliptical rotating magnetic filed generated by the stator 100 is transmitted to the permanent magnet rotor 150, which causes the permanent magnet rotor 150 to be rotated. While the permanent magnet rotor 150 is rotated, a rotating magnet field having a high magnetic flux is generated. The induction rotor 120 is rotated by the rotating magnetic field having the high magnetic flux and thus the rotating shaft 140 is rotated. Accordingly, the induction motor in accordance with the conventional art can be operated making a low noise by rotating the induction rotor 120 by the rotating magnetic field having the high magnetic flux generated when the permanent magnetic rotor 150 is rotated.
However, in the induction motor in accordance with the conventional art, since the power (AC) is directly applied to the stator coils 160A, 160B, 160C and 160D connected in series, a magnetomotive force is reduced when the induction motor is initially driven, and thus the induction motor cannot be swiftly driven at the initial stage because the magnetomotive force is reduced. That is, the induction motor in accordance with the conventional art is driven with high efficiency after its initial driving by directly applying the power to the stator coils 160A, 160B, 160C and 160D, but it has a problem that the induction motor cannot be swiftly driven due to the low magnetomotive force when the power is initially applied to the induction motor. For example, when the power is directly applied to the stator coils 160A, 160B, 160C and 160D, the induction motor is driven with high efficiency after its initial driving. However, when the induction motor is initially driven, since a current less than required current for the driving is applied to the stator, the magneto motive force is reduced, and thus the induction motor cannot be swiftly driven at the initial stage because the magnetomotive force is decreased.
Meanwhile, the induction motor in accordance with the conventional art is also disclosed in U.S. Pat. Nos. 6,700,270 and 6,445,092.